1. Field of the Invention
The present invention relates to a time-of-flight mass spectrometry system for measuring the mass of sample ions based on the time of flight of an ionized sample to a detector, and a charged particle detecting apparatus to be used therefor.
2. Related Background Art
Time-of-flight mass spectrometry systems (TOF-MSs) that ionize samples and perform mass spectrometry based on differences in the flight time thereof have been known. As a typical TOF-MS, a spectrometer of the type disclosed in JP 2001-503196 A has been known.
In the TOF-MS, as shown in FIG. 19, a detector 100 is arranged at one end in a vacuum vessel 110, a sample 120 is arranged at the other end, and an electrode 130 having an opening is arranged between them. When the electrode 130 is grounded and a predetermined voltage is applied to the sample 120, ions emitted from the sample 120 are accelerated by an electric field formed between the sample 120 and the electrode 130, and collide with the detector 100. Because the acceleration energy to be given to the ions between the sample 120 and the electrode 130 is determined according to ion charge, the speed when ions pass through the electrode 130 depends on the mass of ions if the ion charge is the same. Between the electrode 130 and the detector 100, ions fly at a constant speed, so that the flight time of the ions therebetween is in inverse proportion to the speed. That is, the mass of ions can be determined by calculating the flight time therebetween.
As that detector 100, a detector of the type disclosed in JP3132425U, U.S. Pat. No. 5,770,858A, and JP2007-87885A. A basic equivalent circuit diagram is shown in FIG. 20. The detector 100 uses two disk-like microchannel plates (MCPs) 20 and 21 as an MCP group 2, and has a construction where an IN electrode 1 is arranged on its charged particle incident surface, an OUT electrode 3 is arranged on its exit surface, and the IN electrode 1 and the OUT electrode 3 sandwich the MCP group 2 therebetween. Behind the OUT electrode 3, an anode substrate 40 is arranged at a predetermined distance. In the detector 100 disclosed in these documents, a flange to be mechanically connected to the anode substrate 40 has been used to fix on a spectrometry system such as a TOF-MS.